Flexible, rolling film belts are finding increasing acceptance as an alternative to bulkier, and non linear, swinging doors. A typical system uses a belt with one or more apertures that rolls back and forth from a powered wind up roller onto a passive, take up roller. Any fraction of the belt aperture can be aligned with a duct or frame opening to achieve a corresponding degree of air flow. A flat belt is also inherently more compact than a swinging door.
Newer automotive HVAC systems often provide for multi zone (individual occupant) air flow rate or temperature control, or both. To achieve independent control with a film belt system, separate film belts capable of at least substantially independent movement are required. Typically, this would also require a separate drive motor to turn the wind up roller of each belt. The motor is one of the more expensive and space consuming elements of the system.